Opaquing agents for vitreous enamels and process of making



B. w. KING, JR. ETAL 2,555,272 OPAQUING AGENTS FOR VITREOUS ENAMELS AND PROCESS OF MAKING 2 Sheets-Sheet 1 m w, w

May 29, 1951 Filed April 6, 1949 m MILLIMIGRONS 0/: Enamel In MILLIMICRONS Oefermmaf/an; m Enamel 47 1h fnf 40 jmz/sy/f.

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WA VEL ENG TH 5 )0 Peri can) 5/0 above sfandara Patented May 29, 1951 OPAQUING AGENTS FOR VITREOUS ENAMELS AND PROCESS OF MAKING Burnham W. King, Jr., Shaker Heights, and Lofton C. Baumhardt, Elyria, Ohio, assignors to The Harshaw Chemical Company, Cleveland, Ohio, a corporation of Ohio Application April 6, 1949, Serial No. 85,828

7 Claims. (01. 106-312) and titanium or zirconium, together with suitable fluorides, and calcination products thereof. In U. S. Patent No. 2,033,707 to Harshaw and Stillwell, similar compositions were described, however, not including fluorides. U. S. Patents 2,306,356 and 2,306,357 disclose further improvements in'composition proportions and methods of manufacture of opaquing agents of the type indicated in the earlier patents referred to. It is to improvements in the type of opaquing agents disclosed in these prior patents that the present invention relates.

We have now discovered that certain advantages can be gained by adding a small proportion of silica or calcium silicate to compositions of the type indicated. Inasmuch as these materials are relatively cheap, it is obvious that any proportion thereof which can be used will represent a saving in cost of raw materials and, since the quality of the product is improved, the substitution is very attractive. Depending upon the degree of opacity required in the final enamel, the weight of the coating and the percentage of mill addition as well as other factors, a greater or less amount of silica can be tolerated. For some purposes as much as or 12% can be used before the total reflectance becomes too low and the enamel becomes too hard. Based solely upon the factor of reflectance, the addition of silica would be justified only between 4% and 6%; but there are, surprisingly, other and quite important factors. We note that the silica makes possible a harder and shorter fire and results in an improvement in color best described as a shift toward the blue, that is, an elevation of the reflectance in the blue end of the spectrum sometimes accompanied by a depression in the red. This latter factor justifies the addition in some cases of the larger amounts up to 10% or 12%. A further important factor is the ability to use somewhat less pure raw materials without impairment of color.

' In the accompanying drawings, Fig. 1 is a diagram wherein are reproduced spectropho- Such opaquing agents are of tometer charts (Hardy) of three representative compositions, in the form of powder, two of which areaccording to the invention and the other of which is called a standard composition, being the one which has been most commercialized heretofore; Fig. 2 is a similar diagram wherein are reproduced spectrophotometer charts of enameled sheet metal plaques opacified with the above described standard and one of the compositions according to the invention; Fig. 3 is a diagram wherein are plotted total reflectances against per cent silica added, the reflectance of the standard being taken as the zero value; Fig. 4 is a diagram wherein are reproduced spectrophotometer charts (on powder) of compositions one of which is the example from U. S. Patent 2,200,170, page 3, column 2, lines 35 to 40 and the other of which is identical except that for the MgSiFe there has been substituted the molecular equivalent of MgFz; Fig. 5 is a similar diagram showing spectrophotometer charts (on powder) of compositions made under identical conditions except that one has no Si02, one has SiOz added as such and the other has SiOz added as OaO.SiO2; and Fig. 6 is a diagram showing the results when the compositions of Fig. 5 are made up into enamel and applied on steel plaques.

The composition of the final product, on the analytical basis, may be as follows:

Preferred compositions are as follows:

813205, 0.95 to 1.15 molecular weights.

CaO, 3.3 to 4.1 molecular weights.

CaFz, 0.45 to 0.6 molecular weight.

T102, 275 to 3.5 molecular Weights.

(From 0.4 to 0.6 molecular weight of T102 may be replaced by ZrSiOi.)

SiOz, to 12% of the combined weights of the other ingredients. It is preferred to use 4% to 6% SiOa.

Various materials may be used as sources for the above constituents of the final product. We prefer to use SbzOa, Sb204 or Sb205 as the source S102, added as 8102, or

CaO.SiO2

3 of antimony, CaO, Ca(OH)2 or CaCOa, as the source of lime, fluorspar or other CaFz as the source of fluorine, T102 as such, and S102 as such or as CaO.SiO2. Such materials as will yield SiOz, as such, under the conditions of calcination and without yielding harmful contaminants presumably could be used. We found, however, that MgSiFe did not give the desired result, whether because it does not yield S102 or for what reason.

we do not know. The efiect of SiOz in ZrSiOiis noticeably beneficial but only part of it seems to be eifective, and since but little'ZrSiOli is used in any formula, we neglect this source or merely use a little less SiOz or CaOSiOz in the'zirconcontaining compositions. We have found that S102 and CaO.SiO2 are suitable sources of SiOz. Since calcium silicate exists invarious ratios of 02.0 and S102, the CaO content should, when calcium silicate is used instead of S 2, replace an equal amount of Ca(O'H)2 or CaCOs and the SiOz content. should replace an equal amount of SiO2.

Examples I, II and III are suitable batch compositions; while Examples IV, V and VI are special comparisons illustrating the effect of the invention.

Example I Parts by weight CaCOa 300 Ca(OI-I)2 37 CaFz 39 SbzOs 291 TiOz 24:0 SiO2 45 Example-II Parts by weight CaCO3 300 Ca(OI-I)2 3'7 CaFz 39 513203 29 1 T102 240 SiQz 90 Example I-II Parts by weight. CaCOz 300 Ca(OH)z 37 CaFz 39 SbzOs 291 T102 200 ZI'SiO4 (zircon) 91 S102 67 Example 11V Two batches were made up in weight proport'ions as follows:

100 100 8: 168.6 168. 6 TiOL 240.3 240.3 smol MgSiFn HNOflconc) 80.0 80.0 MgF 30.0

furnace temperature for a period of 3 hours, reaching a maximum of 1110 C. The batch temperature was between 1000 C. and 1110 C. for about 3 hours and above 1100 C. for about 1 hour. Spectrophotometer measurements were made on the resulting powder with the results shown in. Fig. 4-.

It can be seen that batch 2 is higher in the Violet end of the spectrum and lower in the yellow and red than batch 1. Batch 2 thus has a bluer tint than batch 1. Both samples are low in the violet and are creamy, but batch l is definitely more yellowish than batch 2. Thus, the SiF4 content of the MgSiF4 was not effective to reduce the yellow component of the color.

Example V Three batches were made up in weight proportions as follows:

Numbers in parentheses in the above table are the molecular proportions, each indicating the number of molecular weights represented by the numbers under which they appear. Other numhere are parts by weight. These batches were calcined under similar conditions to those described under Example. IV. Spectrophotometric curves were run on the resulting powders with the results shown in Fig. 5,

It will be seen that batch; 2 isidentical with batch 1 with the exception that 45 grams of S102 have been added. Batch 3 is identical with batch 1 with the exception the 87.5 grams (0.75 mol) of CaOiSiOZ have been added and the CaCO3 content ha s been reduced by 0.75 mol. The'SiOzv content of the CaOSiOz is 45' grams as in batch 2.

Example VI The batches of Example V; were made into enamel slips, using the same frit and all other factors being identical as far as-possible. The slips were applied to: steel plaques and fired.

Spectrophotometer charts were taken from the; resulting enameled plaques and-with the results shown in Fig. 6.

In the practice of the invention, calcination is carried; out at a temperature preferably from 1000" C. to 1200 C., batch temperature, in an; oxidizingv atmosphere The time required variesaccording to thetemperatureand other conditions, particularly thesize of the batch, larger batches requiring-longer time. The reflectanceis nearly fully developed by l hours firing at 1150 0., whereas threeto five or more hoursare complete the firing as quickly ashecan without sintering the product, although longer firing does no harm.

It will be understood that, consistent with the foregoing statements concerning suitable batch temperatures, in plant practice the firing cycle includes a period for bringing the temperature up to the desired firing range, a periodin the desired range and a cooling down period. Preferred'plant practice for the silica-free product was 6 hours at a temperature below1000 CL, 6 hours above 1000 C. reaching a maximum of 1100 C. and 7 hours below 1000 C. down tothe end of the cycle at 40 C. The current preferred practice, using silica in the formula is a firing cycle requiring 4 hours heating below 1000 C., 4% hours above 1000 C. reaching a maximum of 1150 C. and hours cooling from 100,0 C. down to the end of the firing cycle of 40 C. It will thus be seen that the preferred firing cycle has been reduced from about'19 hours to about 13 hours, the quality of the product not being reduced by the harder firing but actually being improved thereby. In each case the plant practice has been to fire as hard as could be done safely, that is, without danger of sintering. By hard firing we do not mean that the maximum temperature is increased but that the increase in furnace and consequently batch temperature is more rapid in the early-stages so that maximum temperatureis attained earlier in the cycle.

The above comparative firing cycles from plant practice are stated in terms of kiln temperatures (tunnel kiln) and it will be understood that batch temperatures lag somewhat behind kiln temperatures.

The above described compositions which contain S102 added as such or as CaO.SiO2 are suitable for use as mill additions and preferably are incorporated into enamel slips at 2% to and usually at 4% to 6% at the mill. The composition of Example III is most suitable for use with zirconium-containing frits.

By reference to Fig. 2 it will be seen that the composition disclosed in Example I, omitting all S102, has the color indicated by the heavy line while the composition of Example I as set forth without any omission has the color indicated by the dotted line. It will be noted that the composition to which silica has been added is relatively high in the blue and less high in the red. Numerous samples have been run and this change in slope or increase in blueness was found to be characteristic from to 12% and even higher although the higher values were not investigated to any substantial extent because of the hardness of the resulting enamels. In Figs. 4 and 5 we have shown spectrophotometer charts taken on the'powders rather than on enamels. These views show the increase in blueness. The increase in opacity shown in Fig. 1 follows approximately the trend indicated in Fig. 3. It should be explained that the points shown in Fig. 3 are averages of about 10 determinations per batch and on from two to seven batches. The refiectances are variable from batch to batch because of the diificulty in obtaining uniform calcining conditions on the various samples and a number of other lesser factors such as variability of raw materials, application, weight, etc. Individual variations up to about 1% in total reflectance were encountered in the range from 1 to 5% S102 and up to about three per cent in the higher ranges up to 20% SiOz. This variability'is' illustrated by the table below which contains the data upon which Fig. 3 is based.

Notwithstanding the variability exhibited by the samples upon which the table is based, there is a consistent dip at 3%, a consistent maximum at 5 and a downward trend from about five per cent to 20%. Spectrophotometer curves were run on most of the plaques upon which the table is based and they consistently show the shift of the color toward the blue. The shift is consistently of the order shown in the drawings. 7

By the expression theoretical composition as used in the claim, we mean the composition which should be found on analysis, based upon the assumption that C'aCOa and Ca(OH)2 break down completely to CaO and volatile CO2 and H20; that CaFz remains unchanged, that T102 and ZrSiO4 remain unchanged if present in the batch; that SbzOa and SbZOl are oxidized to SbzOs; that CaO.SiO2 either breaks down to C'aO and S102 or remains unchanged. The use of this expression is not intended to define the state of association of the component oxides. Reactions may and probably do take place, and some of the material may be in a state of solid solution.

This application is a continuation-in-part of our copending application Serial No. 759,226, filed July 5, 1947, now abandoned, which was a continuation-in-part of our application Serial No. 722,741, filed January 17, 1947, now abandoned.

Having thus described our invention, what we claim is:

1. A new composition of matter suitable for use as a mill addition opacifier for vitreous enamels, the same being the product of calcining under oxidizing conditions an antimony compound of the class consisting of SbzOa, $13204 and Sb20s, a calcium compound of the class consistin of (32.0, Ca(OH)z and CaCOz, CaFz, T102 and a silicon compound of the class consisting of S102 calcium silicate, said compounds being em.- ployed in proportions to yield a calcination product of theoretical composition as follows:

SbzOs, 1 molecular weight,

CaO, to mol per cent 3 to 5 molecular CaFz, up to 15 mol per cent Welghts T102, 2 /2 to 3 /2 molecular weights, S102, to 12 of the other components by weight.

in proportions to yield a calcination product of: theoretical composition as follows:

Sb205, 0.95 to 1.15 molecular weights,

CaO, 3.3 to 4.1 molecular weights,

CaFz, 0.45 to 0.6 molecular weight,

TiO2, 2.75 to 3.5 molecular weights,

$102, 4% to 6% of the other components by weight.

3. The composition asdefined wherein from 0.4 to 0.6 molecular weight of T102 is replaced'by the'molecular equivalent of a com.- pound of the class consisting of ZIOz and ZrSiOr.

4. A process for'the production of a new composition of matter suitable for use as a mill addition opacifier for vitreous enamels comprising calcining under oxidizing conditions in the temperature range from 1000 C. to 1200 C. for from 1 to 6 hours an antimony compound of the class consisting of SbzOa, Sb204 and Sb205, a calcium compound of the class consisting of CaO, Ca(OH)2 and CaCOs, CaFz, T102 and a silicon compound of the class consisting of SiOz and calcium silicate, said compounds being employed in proportions to yield a calcination product of theoretical composition as follows:

Sb205, 1 molecular weight,

CaO, 85 to 100 mol per cent 3 to 5 molecular ts, CaFz, up to 15 mol per cent welgh TiO2, 2 /2 to 3 /2 molecular weights, 7 $102, /2% to 12% of the other components by weight.

in claim 2 5-. A processfor the. production of a new com,

position ofmatter suitable'for use-as a mill aqdi- Sb205, 0.95 to 1.15 molecular weights,

CaO; 3.3 to 4.1 molecular weights,

CaFz. 0.45 to 0.6 molecular weight,

TiOa; 2.75 to 3.5 molecular weights,

Si02, 4% to 6% of the other components by weight.

6. The process as defined in claim 4 wherein from 0.25 to 1.0 molecular weight of T102 is.r.e,- placed by the molecular equivalent of a compound of the class consisting of ZrOz and ZrSiO4.

7. The process, as defined in claim 5 wherein from 0,4 to 0.6m0lecu1ar weight of T102 is re.- placed by the molecular equivalent of a compound of the class consisting of ZIOz and ZrSiOi.

BURNHAM W. KING, JR- LOFTON C; BAUMHAR D' I.

No references cited. 

2. A NEW COMPOSITION OF MATTER SUITABLE FOR USE AS A MILL ADDITION OPACIFIER FOR VITREOUS ENAMELS, THE SAME BEING THE PRODUCT OF CALCINING UNDER OXIDIZING CONDITIONS AN ANTIMONY COMPOUND OF THE CLASS CONSISTING OF SB2O3, SB2O4 AND SB2O5, A CALCIUM COMPOUND OF THE CLASS CONSISTING OF CAO, CA(OH)2 AND CACO3, CAF2, TIO2 AND A SILICON COMPOUND OF THE CLASS CONSISTING OF SIO2 AND CALCIUM SILICATE, SAID COMPOUNDS BEING EMPLOYED IN PROPORTIONS TO YIELD A CALCINATIN PRODUCT OF THEORETICAL COMPOSITION AS FOLLOWS: SB2O5, O.95 TO 1.15 MOLECULAR WEIGHTS, CAO, O.3 TO 4.1 MOLECULAR WEIGHTS, CAF2, O.45 TO 0.6 MOLECULAR WEIGHT, TIO2, 2.75 TO 3.5 MOLECULAR WEIGHTS, SIO2, 4% TO 6% OF THE OTHER COMPONENTS BY WEIGHT. 